The term ‘computing device’ includes, without limitation, Desktop and Laptop computers, Personal Digital Assistants (PDAs), Mobile Telephones, Smartphones, Digital Cameras and Digital Music Players. It also includes converged devices incorporating the functionality of one or more of the classes of device already mentioned, together with many other industrial and domestic electronic appliances.
An increasing number of these devices are mobile and battery-operated, and proper management of power resources and power consumption on the device is critical for ensuring that power is not wasted, and that the user gets a reasonable and respectable amount of use out of one set of batteries or one charge of the internal batteries.
Power resources in computing devices may vary in complexity, from simple binary resources that can be switched on or off almost instantaneously to resources that can be set at different voltage levels or that take a definable time period to change state. There are also resources that may only be changed in conjunction with other resources.
Overcoming the power constraints of a mobile computing device can be done in a number of ways. These include                producing and using batteries with a higher storage capacity        producing and using components which consume less power for a particular task; for example, mobile music devices can be provided with headsets that require less power to produce a given level of sound to a user in comparison to the use of loudspeakers.        reducing the power consumed by components reserved for certain tasks or applications; for example, the user of a mobile music device can reduce the signal output level to their headset in order to conserve power. Another example is the way mobile telephones can reduce their transmission power down to the minimum necessary to communicate with a base station.        
Recent innovations in the design of mobile computing devices, notably mobile telephones, define a number of shared software-definable power resources, such as clock frequencies, variable voltages and switchable power rails. However, the fact that shared power resources contained within a computing device can operate at many levels has not yet been taken into account for efficient power management. There is a need for intelligent management of these multilevel shared power resources. Because they are shared, and are not reserved for specific applications, this control is best handled as part of the operating system (OS) that has overall control of the hardware and the software in the device.